The comet was listed on the near-Earth object confirmation page (NEOCP) as gb00234 because orbit solutions had the possibility of it making notable approaches to Earth. Before the uncertainties were reduced enough to know the comet was hyperbolic (e>1) and 3 au from the Sun, orbit solutions suggested it could be 1.4 au from the Sun, have an aphelion (furthest distance from the Sun) of 1.6 au, and orbit the Sun in less than 1 year.[12] Such a solution came from exchanging eccentricity for inclination, ie: higher inclination of 75° with a lower eccentricity of 0.7. Such an orbit is now known to be invalid.

The smaller the perihelion point, the smaller the eccentricity will be.[13] Interstellar flybys can have very high eccentricities such as e > 3 because the objects were never bound to the Sun and a small change in velocity will result in a large change in the eccentricity.

With a 13-day observation arc, a best-fit for the hyperbolic orbit has an eccentricity of about 3.5, with perihelion at 2.0 au around 7 December 2019.[2] Using 151 observations, JPL's Scout gave an eccentricity range of 2.9–4.5.[3]

With an observation arc of only 12 days, there was still some doubt to if it was interstellar. But the orbit could only be parabolic if it is significantly affected by non-gravitational forces (outgassing thrust) more than any other known comets.[9] Using large non-gravitational forces on the highly eccentric orbit solution could generate an eccentricity of about 1, an Earth-MOID of 0.34 au (51 million km), with perihelion at 0.90 au around 30 December 2019.[14] But the orbit converged to the hyperbolic solution which indicated an interstellar origin and non-gravitational forces could not explain the motion.[5]

Currently it is a better northern hemisphere object.[2] Due to the 44 degree orbital inclination, C/2019 Q4 does not make any notable close approaches to the planets.[1] Around 6 December 2019 the comet will be an equal distance from the Sun and Earth.[2] In late December it will be about 2 au from Earth and have a solar elongation of about 80°.[2] By the new year it will be a better southern hemisphere object.[2]

The higher hyperbolic excess velocity of C/2019 Q4 of 30.7 km/s makes it harder to reach for a spacecraft than 1I/'Oumuamua (26.33 km/s). According to a team of the Initiative for Interstellar Studies, a two-ton spacecraft could theoretically have been sent in July 2018 to intercept with C/2019 Q4 using a Falcon Heavy-class launcher, but only if the object had been discovered much earlier than it was.[18] Launches after the actual discovery date would require a significantly large launcher such as the Space Launch System, a combined Jupiter flyby and an Oberth manoeuvre. And even a SLS-class launcher would now only be able to deliver a 3kg payload (such as a CubeSat) to a trajectory that intercepted C/2019 Q4. According to congressional testimony, NASA may need at least five years to launch such an intercepting mission.[19]

On 13 September 2019, the Gran Telescopio Canarias obtained the visible (low-resolution) spectrum of C/2019 Q4 (Borisov) that revealed that this object has a surface composition not very different from that found in typical Oort Cloud comets.[20]

^Comet Elenin was inbound 200 AU from the Sun on 1798-Sep-29. Computed using JPL Horizons Observer Location: "@sun" (deldot is relative motion in km/s and a negative deldot means the target is moving toward the observer.)